21393839 has 4 divisors (see below), whose sum is σ = 21473640. Its totient is φ = 21314040.

The previous prime is 21393809. The next prime is 21393847. The reversal of 21393839 is 93839312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21393839 - 2⁸ = 21393583 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21393809) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 39497 + ... + 40034.

It is an arithmetic number, because the mean of its divisors is an integer number (5368410).

Almost surely, 2^21393839 is an apocalyptic number.

21393839 is a deficient number, since it is larger than the sum of its proper divisors (79801).

21393839 is an equidigital number, since it uses as much as digits as its factorization.

21393839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 79800.

The product of its digits is 34992, while the sum is 38.

The square root of 21393839 is about 4625.3474464088. The cubic root of 21393839 is about 277.6064640327.

The spelling of 21393839 in words is "twenty-one million, three hundred ninety-three thousand, eight hundred thirty-nine".